Method of making an insulation foil

ABSTRACT

An insulating foil particularly adapted for use in a multilayer insulation system is disclosed together with a method of making such insulation. A molten ceramic material such as a refractory oxide is deposited on a plurality of spots on a metal foil to produce protuberances having a ceramic coating. This may be accomplished by plasma spraying the material through an apertured mask placed against the foil. The foil may be in the form of a continuous strip which is advanced to a new position after each flame spraying operation. A cooled backing plate may be disposed against the foil to control the temperature thereof. Hydraulic actuating means may be utilized to actuate the apertured mask to clamp the foil between the mask and the backing plate prior to each flame spraying operation.

Unite States atent 1191 Maslowski Sept. 23, 1975 [54] METHOD OF MAKING AN INSULATION 3,193,408 7/1965 Triller 117/38 X FOIL I 3,197,335 7/1965 Leszynski..

3,647,533 3/1972 Hicks 117/38 X [75] Inventor: Edward A. Maslowski, Seven Hills,

Ohm Primary Examiner-William D. Martin [73] Assignee: The United States of America as Assistant Examiner shrive Beck represented by the United States Attorney, Agent, or FirmN. T. Musial; J. A. Mackin; National Aeronautics and Space Mannmg Administration Office of General Counsel, Washington, DC. ABSTRACT [22] Filed: May 2, 1973 An insulating foil particularly adapted for use in a multilayer insulation system is disclosed together with [21] App1.No.: 356,554 a method of making such insulation. A molten ceramic material such as a refractory oxide is deposited 52 us. (:1. 72/46; 117/38; 117/46 FS; a plurality Spots f Pmduce 117/1052; 117/85; 29/5272; zg/Dlo 24; tuberances havmg a ceramic coatlng. This may be ac- 29/D[G 39 compllshed by plasma spraying the mater al through 51 1m. (:1 B44d 1/40; B44d 1/52 aperiumd mask Placed agamst 1? [58] Field of Search 117/85, 38, 46 PS, 105.2; may be m the Mm a cmtmmus Smp 72/46 29/5272 DIG 24 DIG 39 vanced to a new position after each flame spraying operation. A cooled backing plate may be disposed [56] References Cited against the foil to control the temperature thereof. Hy-

draulic actuating means may be utilized to actuate the UNITED STATES PATENTS apertured mask to clamp the foil between the mask l and the backing plate prior to each flame spraying ope1 on 2,775,531 12/1956 Montgomery et a1. 117/46 FS eranon 2,874,065 2 1959 Herz et a1. 117/1052 9 Claims, 2 Dr g g r US Patent Sept. 23,1975

FIG. 2

1 METHOD OF MAKING AN INSULATION FOIL ORIGIN OF THE INVENTION The invention described herein was made by an employee of the United States Government and may be manufactured and used by or for the Government of the United States of America without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION separating and which includes barriers to thermal conductance between adjacent layers.

It is a further object of the invention to provide a foil of the foregoing type and a method of making such foil ment in recent years because their light weight makes them very advantageous for use in space vehicles, for example, where weight considerations are extremely important. Such insulation systems are, of course, very useful for other applications such as retaining heat in metallurgical vacuum furnaces or for insulating extremely cold materials such as liquid nitrogen or liquid hydrogen.

In general, a multilayer insulation consists of. many layers of radiation-reflecting shields or foils separated by low thermal conductivity spacers. The spaces between the shields may be evacuated to decrease thermal conduction which would exist if a gas such as air were present. Prior art foils or shields for multilayer insulation have been made by either crinkling, dimpling or embossing the foil so that minimal contact is made between adjacent layers of foil; coating the foil with a low thermal conductivity material; or, interposing a low conductivity material as, for example, cloth or fibrous matting between the layers on the foil.

The crinkled or the embossed foil is simple, clean and inexpensive to make. However, it has a serious disadvantage in that there is a direct metallic contact between the crinkles or embossed portions of one foil and the adjacent foil. This allows high thermal conduction between the foils resulting in a solid conduction efflcieney loss which is related to the contact pressure between the foils.

Low conductivity coatings applied to the foil as, for example, by flame spraying result in lower solid conducting losses. Such coatings are relatively brittle and, when applied to large areas of foil, tend to disintegrate. They also lower the reflectivity of the foil which consequently reduces efficiency.

A major disadvantage of a multifoil insulation in which mats are disposed between the layers of foil is that the thickness of the multifoil insulation system is considerably increased because the mats are relatively thick. Additionally, material placed between the foils may serve as a source of outgassing which could damage the foils.

OBJECTS AND SUMMARY OF THE INVENTION It is an object of the invention to provide an improved insulating foil which may be utilized in a multifoil insulation system, together with the method of making such foil.

It is another object of the invention to provide a re flective foil which, when arranged in layers, is self- 12. The foil is maintained in contact with a backing.

wherein barriers which are provided against thermal conduction cause only a minimal reduction in a reflective area on the foil.

An additional object of the invention is to provide a method of producing a reflective foil which is both embossed and provided with thermal conductance barriers in one operation.

Still another object of the invention is to provide a foil which can be utilized to make a multifoil insulation system of low weight and high reflectivity and having a greatly reduced number of layers as compared to multifoil insulation systems of the prior art.

Yet another object of the invention is to provide a reflective foil processed in such a manner that, when used in a multifoil insulation, the contact area between adjacent layers of foil is minimal and in which the thermal conduction of heat at the contact areas is minimal.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows apparatus for processing a reflective foil in accordance with the invention.

FIG. 2 is a cross sectional view of two layers of a mu]- tifoil insulation utilizing foil made in accordance with the invention.

DESCRIPTION OF THE PREFERRED I EMBODIMENT Referring now to FIG. 1, there is shown a foil strip 10 which is drawn from a supply roller 11 by a drive roller plate 13 by means of a tension roller 14. To the end that the foil 10 will be maintained in a predetermined temperature range a coolant, such as water or any other suitable liquid, is supplied through an input conduit 15 to the backing plate 13 which may be hollow or which may contain passages for the coolant. The coolant is exhausted from the backing plate 13 by means of an outlet conduit 16.

To the end that ceramic-coated proturberances will be formed on the foil 10, a mask such as apertured plate 17 is first disposed against the front surface of foil 10. Then a refractory oxide is flame sprayed onto foil 10 through the apertures of the mask 17 by a flame spray gun 18. It .will be understood, of course, that traverse velocity of the flame spray gun 18 is dependent upon the material of the foil 10, the material being flame sprayed, and the size of the apertures in the mask 17. These parameters may be determined experimentally because of the number of variable involved, such as the thickness of the foil, the materials used and the size of the apertures.

In the apparatus shown in FIG. 1 the mask 17 is held in a frame 19. A hydraulic actuator 20 moves the frame 19 and the apertured plate 17 away from the foil 10 after each flame spraying operation. The foil 10 is then advanced to the next position and the hydraulic actuator 20 causes the apertured plate 17 to again contact the foil 10, clamping it between the mask 17 and backing plate 13. Coolant may also be circulated through plate 17, if desired, by means of connections as used with plate 13.

The apertures in mask 17 may range in diameter from about 0.05 inch to 0.25 inch, with 0.1 inch being the preferred size. The number of aperatures to be provided is determined by the size of the apertures together with the desired ratio of the area of the spots to be coated to the uncoated reflective area. This ratio is preferably less than one; that is, the coated spots cover less than fifty percent of the foil for a sample area which includes a sufficiently large number of spots, ten in number for example. Practical considerations deter mine that the ratio be no smaller than 1 to 16, with a ratio of about 1 to being generally preferred.

Referring now to FIG. 2, there are shown two foil layers 10, each having protuberances which are coated on their uppermost portion with a ceramic 21. The protuberances 20 provide spacing between the foils 10.

The protuberances 20 are caused by thermal stresses which occur in the foil when the molten ceramic material is deposited on it at each aperture in the mask 17. The ceramic material 21 may contain voids or discontinuities due to thermal stresses or to the nature of flame spraying. However, these voids or occlusions do not adversely affect the efficiency or performance of the foil because the ceramic material serves its purpose of avoiding direct metallic contact between adjacent foils.

The foil 10 is not limited to any particular thickness except that it must be thin enough so that when molten ceramic is applied to spots on the foil, the resulting thermal stresses at those spots will produce ceramic coated protuberances. However, for mutlilayer reflective foil insulation systems, a foil thickness of from about /2 mil (0.0005 inch) to about 2. mils (0.002 inch) is generally preferred. The foil 10 may be made of materials such as aluminum, copper, molybdenum, nickel, niobium, stainless steel, tantalum and tungsten, although use of the invention is not limited to these particular materials. Preferably, the ceramic to be deposited on the foil is selected from the refractory oxides including aluminum oxide, beryllium oxide, thorium oxide and zicronium oxide.

From the foregoing, it will be seen that the invention provides a self-spacing, thermal barrier, reflective insulation foil. This foil is made by depositing molten ceramic material on a plurality of spots on a metallic foil to produce oxide coated protuberances.

It will be understood that those skilled in the art may make changes and modifications to the foregoing described invention without departing from its spirit and scope, as set forth in the claims appended hereto.

What is claimed is:

l. A method of producing self-separating, thermallyinsulating, reflective sheets comprising the step of:

depositing a molten ceramic material onto a plurality of spots on a reflective metallic sheet having a thickness such that thermal stresses occur at each spot to produce a protuberance substantially covered with a ceramic coating.

2. The method of claim 1 wherein said metallic sheet is a foil from about /2 mil to about 2 mils thick.

3. The method of claim 1 wherein for any given area of foil encompassing at least 10 spots the ratio of the area of said spots to the remaining uncoated area is less than one. 7

4. The method of claim 1 wherein said metallic sheet is selected from the group consisting of aluminum, copper, molybdenum, niobium, stainless steel, tantalum and tungsten.

5. The method of claim 1 wherein said ceramic material is a refractory oxide selected from the group consisting of aluminum oxide, beryllium oxide, thorium oxide and zirconium oxide.

6. The method of claim 1 wherein an apertured mask is disposed against a first surface of said metal sheet to define the spots to be thermally stressed and coated and the molten ceramic is deposited by flame spraying through the apertures of said mask.

7. The method of claim 6 wherein a cooled backing plate is placed against the other surface of said metal sheet prior to flame spraying to prevent excessive temperature rise in said metal sheet.

8. The method of claim 1 wherein said metallic sheet is a continuous, normally-moving strip and including the steps of:

stopping said strip;

clamping said strip between an apertured plate and a heat-absorbing backing plate;

flame spraying a ceramic material on said strip through said apertured plate;

declamping said strip from between said apertured plate and said backing plate; and

advancing said strip to a new position.

9. The method of claim 1 wherein the ceramic coating is less than one-tenth mil thick. 

1. A METHOD OF PRODUCING SELF-SEPARATING, THERMALLY-INSULATING, REFLECTIVE SHEETS COMPRISING THE STEP OF: DEPOSITING A MOLTEN CERAMIC MATERIAL ONTO A PLURALITY OF SPOTS ON A REFLECTIVE METALLIC SHEET HAVING A THICKNESS SUCH THAT THERMAL STRESSES OCCUR AT EACH SPOT TO PRODUCE A PROTUBERANCE SUBSTANTIALLY COVERED WITH A CERAMIC COATING.
 2. The method of claim 1 wherein said metallic sheet is a foil from about 1/2 mil to about 2 mils thick.
 3. The method of claim 1 wherein for any given area of foil encompassing at least 10 spots the ratio of the area of said spots to the remaining uncoated area is less than one.
 4. The method of claim 1 wherein said metallic sheet is selected from the group consisting of aluminum, copper, molybdenum, niobium, stainless steel, tantalum and tungsten.
 5. The method of claim 1 wherein said ceramic material is a refractory oxide selected from the group consisting of aluminum oxide, beryllium oxide, thorium oxide and zirconium oxide.
 6. The method of claim 1 wherein an apertured mask is disposed against a first surface of said metal sheet to define the spots to be thermally stressed and coated and the molten ceramic is deposited by flame spraying through the apertures of said mask.
 7. The method of claim 6 wherein a cooled backing plate is placed against the other surface of said metal sheet prior to flame spraying to prevent excessive temperature rise in said metal sheet.
 8. The method of claim 1 wherein said metallic sheet is a continuous, normally-moving strip and including the steps of: stopping said strip; clamping said strip between an apertured plate and a heat-absorbing backing plate; flame spraying a ceramic material on said strip through said apertured plate; declamping said strip from between said apertured plate and said backing plate; and advancing said strip to a new position.
 9. The method of claim 1 wherein the ceramic coating is less than one-tenth mil thick. 